OBSERVATION OF THE FREEZING LINE IN A DEUTERON GLASS

The phase diagram of the deuteron glass Rb-1-x(ND4)(x)D2PO4 has been d etermined experimentally in the entire range of concentration x. A rec ently introduced temperature-frequency plot has been used to analyze t he shape of the dielectric relaxation spectrum, indicating that in the glassy regime the longest relaxation time diverges according to the V ogel-Fulcher law. The corresponding Vogel-Fulcher temperature has been identified as the static limit of the freezing temperature T-f. The p hase boundaries of the ferroelectric and antiferroelectric phases have been obtained in a standard manner by observing the peaks and breaks, respectively, in the temperature dependence of the quasistatic dielec tric constant. It is shown that in a broad concentration range the obs erved phase diagram can be quantitatively described by a mean-field th eory based on the static random-bond random-field model of dipolar gla sses. The absence of macroscopic polarization in the ferroelectric reg ion close to the glassy phase is probably due to the formation of micr odomains in the presence of local random fields, however, recent NMR d ata suggest that a phase segregation between ferroelectric and glassy regions may occur.